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A dissolved substance, such as a mineral ion, sugar, amino acid, or hormone.

Solute.

The substance that dissolves solutes; water is the main example in plant cells.

Solvent.

The main sugar transported over long distances through the phloem in most plants.

Sucrose.

Proteins embedded in and spanning a membrane that selectively transport substances across it.

Integral transport proteins.

Movement of a solute down its electrochemical gradient without an energy input from the cell.

Passive transport.

Movement of a solute against its electrochemical gradient, requiring an energy source.

Active transport.

The condition in which particles continue moving in both directions across a membrane, but there is no net movement.

Equilibrium.

The combined effects of a concentration difference and an electrical difference on an ion's movement.

Electrochemical gradient.

The voltage difference across a membrane resulting from an unequal distribution of electrical charge.

Membrane potential.

The typical membrane-potential range your professor specifically reviewed, with the cell interior negative relative to the outside.

−60 to −240 mV.

Two gases that can diffuse directly through the lipid bilayer without transport proteins.

Oxygen and carbon dioxide.

Examples of ions whose movement across biological membranes depends on transport proteins.

K+, Na+, and Cl−.

The membrane surrounding the vacuole, across which both passive and active transport occur.

Tonoplast.

The organelle that acts as a solute sink, accumulating solutes and helping establish a gradient that favors water entry.

Vacuole.

Transport proteins that form selective pores, allowing very rapid, passive ion movement down electrochemical gradients.

Ion channels.

Channels that transport positively charged ions, with different types transporting K+, Na+, or Ca2+.

Cation channels.

Channels that transport negatively charged ions, such as Cl−.

Anion channels.

Channels whose opening or closing responds to changes in membrane potential.

Voltage-gated channels.

Channels whose opening or closing responds to the binding of a chemical signal.

Ligand-gated channels.

Channels whose opening or closing responds to physical forces such as membrane stretching.

Mechanically gated channels.

Channels that allow K+ to enter root cells or guard cells when the electrochemical gradient favors entry.

Inward K+ channels.

Channels that allow K+ to leave guard cells or move from xylem parenchyma cells into the xylem.

Outward K+ channels.

Transport proteins that bind a solute, change shape, release it on the other side, and reset; they can transport passively or actively and are generally slower than channels.

Carrier proteins.

A carrier that transports a substance out of a cell, as illustrated by sucrose export and discussed for auxin transport.

Efflux carrier.

Transport proteins that directly use ATP to move substances such as H+ or Ca2+ against their electrochemical gradients.

ATP-driven pumps.

The breakdown of ATP into ADP and inorganic phosphate, releasing energy that can power transport.

ATP hydrolysis.

The pump that moves H+ from the cytosol into the apoplast, helping establish membrane potential and an H+ gradient.

Plasma-membrane H+-ATPase.

The pump that moves H+ from the cytosol into the vacuole, acidifying the vacuole and establishing an H+ gradient.

Tonoplast H+-ATPase.

The pH change caused by an increase in H+ concentration.

A decrease in pH, or acidification.

A pump that produces a net transfer of electrical charge across a membrane; the illustrated ATP-driven cycle uses phosphorylation and changes in protein shape.

Electrogenic pump.

The transport category illustrated by a pump that directly uses ATP to move a solute uphill.

Primary active transport.

Transport that uses energy stored in an ion gradient: one substance moves downhill and drives another substance uphill.

Secondary active transport.

A coupled transporter that moves two different substances in the same direction across a membrane.

Symporter.

A coupled transporter that moves two different substances in opposite directions across a membrane.

Antiporter.

The transporter that uses downhill H+ entry to drive sucrose uptake into a cell.

H+/sucrose symporter.

The plasma-membrane transporter that brings H+ into the cell while moving Na+ out.

Na+/H+ antiporter.

The stomatal response when K+ enters guard cells, solute potential decreases, water enters, and turgor increases.

Stomatal opening.

The stomatal response when guard cells lose K+ and Cl−, solute potential increases, water leaves, and turgor decreases.

Stomatal closing.

The change in guard-cell membrane potential caused by pumping H+ out, which favors K+ entry through inward channels.

The membrane potential becomes more negative.

The change in guard-cell membrane potential caused by Cl− leaving, which helps favor K+ exit through outward channels.

The membrane potential becomes less negative.

The secondary transporter that brings H+ and Cl− into guard cells together during stomatal opening.

H+/Cl− symporter.

The route by which solutes move through cell walls and intercellular spaces.

Apoplastic route.

The route by which solutes move through connected cytoplasm and plasmodesmata.

Symplastic route.

The endodermal barrier that blocks apoplastic movement, requiring solutes to cross a selective plasma membrane before reaching the stele.

Casparian strip.

The transfer of mineral ions from living root cells into the xylem for transport toward the shoot.

Xylem loading.